Shared Resources Laboratories (SRL) are fundamental cornerstones of the 2003 NIH Roadmap. Often referred to as core laboratories, SRLs are the most cost-effective approach to provide a broader range of scientific expertise from skilled technology scientists and advanced instrumentation than would be feasible or economically-viable for individual laboratories. Best practices for a Flow Cytometry SRL include: 1) stable and consistent financial support, 2) a highly qualified scientific director (head), 3) policies conducive to recruitment and retention of highly skilled technical staff, 4) user training and staff continuing education, 5) a quality control program for the instruments, 6) support for research and development, 6) overview of satellite facilities), and 7) at a minimum, a 5-year plan for future technology expansion and operation. The NIA Flow Cytometry Unit is organized and managed in a manner consistent with the policies and staffing levels of flow cytometry cores at extramural academic institutions and at NIH. A survey (updated March 2011) of these sites (9 NIH, 133 academic, total 142) indicates that in 91.4% of the cores, sorting is performed only by core personnel. The reason for this is twofold: 1) it is the most efficient way to provide reliable services to the IRP (i.e. minimizing the possibility of instrument abuse by users and thus removing the cascading effect that this has on the ability to complete the next scheduled users sort, especially when the core is heavily booked). 2) neither the MoFlo nor iCyt are turnkey black box, menu-driven instruments (nor is the Aria II in the case of the ability to troubleshoot). Sort usage has expanded in parallel with instrument capacity. For FY11, the core ran at 102% of capacity. Relevance to the NIA IRP Program In addition to the level of core utilization by investigators, measurement of the effectiveness and value of the core to IRP productivity is evident from the 135 publications (including in press and submitted) generated by NIA investigators using flow cytometry/sorting as an integral part of their research since the cores inception in 1999. Seventy-eight (78) of these publications covers the time span from mid 2005 to the present. A partial list of these includes J Immunology (10), BMC Immunology (2), J Exp Med (1), Cellular Immunology (2), Immunity (1), Nature Immunology (1), Blood (2), Cancer Res (1), PNAS USA (3), Endocrinology (1), PLOSone (3), DNA Repair (3), Mol Cell Biol (3), EMBO J (1), and Nature (1), other journals (43). 98.5% of research papers using core services are from NIA IRP investigators.